import java.util.Scanner;

public class guangai {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int[][] a = new int[100][100];
        int b = in.nextInt();
        int c = in.nextInt();
        int d = in.nextInt();
        int f;
        int e;
        for (int i = 0; i < d; i++) {
            e = in.nextInt();
            f = in.nextInt();
            a[e - 1][f - 1] = 1;
            a[e - 1][f - 2] = 1;
            a[e - 1][f] = 1;
            a[e][f - 1] = 1;
            a[e - 2][f - 1] = 1;
        }
        int v = 0;
        for (int i = 0; i < b; i++) {
            for (int j = 0; j < c; j++) {
                if (a[i][j] == 1)
                    v++;
            }
        }
        System.out.println(v);
    }
}
